DESCRIPTION: (Applicant's abstract) A fundamental characteristic of the CNS is it's ability to integrate information from different senses. This process of `multisensory' or `cross-modality' integration profoundly influences perception and behavior and is most commonly expressed in the facilitated detection, identification, and reaction to combinations of concordant cues from the different senses. It perhaps is most evident when discordant cues are integrated because the perceptual anomalies that result are not only quite striking but lead to incorrect judgments about environmental events. Under some circumstances this can have devastating consequences. This, it is surprising to note that we are quite ignorant about how information from different sensory modalities is synthesized at their convergent site in the CNS, the multisensory neuron. This proposal uses the multisensory neuron of the superior colliculus (SC) as a model to build on previous observations of multisensory integration and to explore its underlying neural processes. We hypothesize an orderly relationship between the characteristics of the various sensory inputs, the nature of their synthesis, and the concomitant changes in SC-mediated behaviors. The first step in testing this hypothesis will involve a quantitative examination of how changes in the physical properties of the stimuli and the response properties of the multisensory neuron itself determine a multisensory product. The next step will be to document the sequence of changes in neural activity that begin with the synthesis of sensory inputs and end with the evocation of premotor signals and overt behavior. There are also at least two circumstances in which multisensory integration may be perturbed as a consequence of disrupting the normal correspondences between the different sensory maps in the brain: deviation of one set of peripheral organs and trauma to a sensory map. Moving one set of sensory organs out of alignment with the others shifts its central map and may produce cross-modality map misalignments. Localized trauma to a given modality's central representation causes long-term reorganizational changes in its map which may also disrupt the alignments among sensory maps. In either case, multisensory integration may be severely compromised. Determining whether intersensory processing is maintained or compromised by damage to or misalignments of peripheral sensory organs, or by trauma-induced reorganizational changes in the brain is of critical importance when considering rehabilitative strategies to deal with impairments of touch, hearing to vision, and the long-term consequences of stroke and head trauma.